The instant invention relates to systems and methods for controlling the actuation of vehicle safety devices and, more particularly, to systems and methods which utilize one or more evaluative measures with which to analyze events possibly requiring actuation of the safety device, wherein each measure is a function of received physical information such as transitory vehicle acceleration information and/or the transitory position of a passenger relative to a fixed structure within the vehicle, and wherein at least one of the measures is accumulated or integrated over time.
A variety of systems and methods for actuating vehicle safety devices are well known in the art. Such systems are used to sense an event: such as a crash condition and, in response to such an event, to actuate an air bag, or lock a seat belt, or actuate a pretensioner for a seat belt retractor. Typically, the safety device is actuated into its protective position when an impact exceeding a predetermined magnitude is detected by the actuating system.
Significantly, known systems and methods for controlling actuation of vehicle safety devices typically rely on changes in one or more estimated physical quantities or crash-discrimination "measures" in determining whether to actuate the safety device. Oftentimes, these evaluative measures are obtained by accumulating values generated from received physical information such as transitory vehicle acceleration information and/or the transitory position of a passenger relative to a fixed structure within the vehicle, as where a vehicle velocity measure is obtained by accumulating/integrating received vehicle acceleration information over time. And, frequently, the function underlying the accumulated measure generates only positive values, as where the measure is representative of accumulated positive jerk (where jerk is the rate of change of the received acceleration information with respect to time, with accumulated positive jerk being useful as representing average clipped jerk) or accumulated variance (where variance is itself a statistical measure of variation among a given number of sampled values, with accumulated positive variance being useful as representing total vehicle crush).
Unfortunately, the use of accumulated measures based on positive-value-only functions have proved highly problematic when encountering certain waveforms. For example, where a given crash waveform includes a resonance component, i.e., where the waveform has a frequency component in the range between about 50 Hz and about 300 Hz, an accumulated measure based on positive jerk or positive variance will become unduly large and, hence, will surpass a predetermined threshold to trigger actuation of the safety device either too early in the crash or responsive to an event not otherwise requiring actuation of the safety device. Stated another way, resonant waveforms can effectively reduce the triggering threshold for a system which employs accumulated measures, with an attendant reduction in the degree of protection afforded to vehicle passengers. A similar effect is produced by so-called "double-hump" waveforms, nominally characterized by large initial acceleration values, moderate intermediate acceleration values, and very large final acceleration values, as might be generated from received acceleration information during a high-speed pole crash due to the collapse of a vehicle crush zone.
And, while the prior art has attempted to overcome the difficulties generated with resonant and double-hump waveforms by accumulating both positive and negative values generated by the measure's underlying function, this approach eliminates the monotonicity of the accumulated measure and, hence, reduces the utility of such measures both in properly identifying the "ON" conditions requiring actuation of the safety device, and the appropriate timing thereof.
What is needed is a system and method for controlling actuation of a vehicle passenger safety device employing an accumulated positive-value-only evaluative measure which is not otherwise susceptible to indicating a false "ON" condition in response to either resonant or double-hump waveforms.